1. Technical Field of the Invention
The present invention relates generally to a torque sensor which may be employed to measure torque transmitted to a steering shaft of automotive electric power steering devices, and more particularly to an improved structure of such a torque sensor which is simple and high in operational reliability.
2. Background Art
Japanese Patent First Publication No. 8-159887 teaches a torque sensor including a magnet and a magnetic sensor. The magnet and the magnetic sensor are so secured to ends of a torsion bar that they are moved relative to each other upon twisting of the torsion bar. The magnetic sensor works to produce an output as a function of the torque applied to the torsion bar.
Japanese Patent First Publication No. 6-281513 teaches a torque sensor which, like the above publication, includes a magnet and a magnetic sensor. The torque sensor also includes a torque converting gear mechanism which works to convert the torsion of a torsion bar into movement of a gear in a longitudinal direction of input and output shafts. The magnetic sensor is secured to a housing, thereby eliminating the need for electric contact parts such as brushes and a slip ring used to supply power to the magnetic sensor and pick up a signal from the magnetic sensor.
The former torque sensor has the magnet and the magnetic sensor connected to the torsion bar, thus requiring electric contact parts such as brushes and a slip ring used to supply power to and pick up a signal from the magnetic sensor, which leads to a greater concern about the reliability of the sensor.
The latter torque sensor has the disadvantage that the backlash or wear of the torque converting gear mechanism may result in error or delay in measurement of the torque.